Treatment of hydrocarbons



May 25., 1943. K. H. HAcHMuTH TREATMENT HYDRCARBONS Filed Sept. 9, 19402 SheetsSheet l 24:5y "nl 7 n B w m W.. A A v m. V/ E mmzbmun f LNWA R Eo v M m .n L l n A nl r 8 6 u 2 m. no. I,

INVENToR KARL H. HACHMLlTl-lv May 25, 1943.

K. H. HACHMUTH TREATMENTA 0F HYDROCARBONS Filed Sept. 9, 1940 2Sheets-Sheet 2 ATTORNY PatentedyMay 25, 1943 UNITED STATESPATENT-ori-'ica TREATMENT F HYDROCARBONS Karl B. Bachmuth, Bartlesville, Okla.,asslgnor to Phillips Petroleum Company, a corporation of DelawareApplication September-9, 1940, Serial No. 356,084 v s cmms (ci.26o-sassi y tion medium used in such a process. I have also Thisinvention relates to the-treatment of hydrocarbons, especially to ltheseparation of heavier low boiling' hydrocarbons from light gases. Itrelates more particularly to the separation of gaseous oleiins fromlighter gases in a step which is used in combination with ahydrocarbon-conversion step.

In'the conversion of normally gaseous parai- `fin hydrocarbons heavierthan methane into normally liquid hydrocarbOnS, it is generally pref?,erable nrst to convert at least apart of the paraffins into olenns, Sucha conversion is always accompanied by the production of appreciableamounts offree hydrogen when carried out directly, and is oftenaccompanied also bythe production of methane. There is considerableproduction of methane when the conversion to oleflns is `completelynoncatalytic, ,especially when substantial .amounts ofpropane or heavierDarains are undergoing conversion, and there is an appreciableproduction of methane when .the conversion is catalytic vandi's'carried' out with rather high extents ofconversion. When thehydrogen is not removed from the mixture i liquids.

In the copending applications of Frederick .E. Frey Serial No.71,7,63'f'lled March 30, v19,36, now Patent 2,314,040, which is 'adivision of his application Serial No. 636,555 filed October 6, 1932,

`and/or methane.

found that when the subsequent production of liquidhydrocarbons is analkylation process that the olen concentration 'in the rich absorptionliquid may be undesirably low, andthat I may increase this olefinconcentration by a suitable novel process to be` more completelydescribed hereinafter. n

It isan object of myinvention to separate normally gaseous hydrocarbonsfrom hydrogen Another object of my invention is to eifect aconcentration of lowI boiling oleins from dilute mixtures containinglower boiling parains.

1A further object ofmy invention is to effect a concentration of` lowboiling olefins from dilute mixtures containing higher boilingparaffins. l

v` Still anotherobjet of myy invention is to use an absorption liquidsuch' as butane and/or I pentane in the concentration of gaseousolefins.

Another object of my invention is 'to pyrolyze ethane and or propane and'recover a free hynow Patent 2,038,834, and Serial No. 82,954 filed June1, 1936, now Patent 2,270,700, it is disclosed that such a separation ofundesired hydrogen and methane from olefin hydrocarbons may beaccomplished in an absorption process using as I have now found thatsuch an absorption and drogen concentrate, an ethylene concentrate. anda highly unsaturated hydrocarbon concentrate comprising hydrocarbons offour and more carbon atoms per molecule.

Further objects and advantages of my invention will become evident fromthe accompanying disclosure and discussion.

'In conventional absorption systems, a gas to be treated is passed to alow point of an absorber and an absorption liquid is passed to a highpoint of the absorber, with allcontact between the absorption liquid andthe gas taking place within the absorber.' In many instances either theabsorption liquid or the gas, or both, are subjected to subatmosphericcooling before being olefin concentration process may b e carried.. outl passed to .the absorber. In some modifications the absorption oil, inits passage down theabsorber, is removed and subjected to ladditionalcooling,` or cooling coils are placed inside the absorberyto veifect aremoval of heat of absorplcarried out moreeiiiclently in two stepsrather than in a single unit. For convenience, the stepsv maybe referredto as'an absorption step and a fractionatingstep, and although thefraction--Vv ating step is adapted to be practiced on what correspondsroughly to a rich absorbent it does not co d to conventionalfractionating steps im a rich absorbent is denuded of the absorbedconstituents, for the liquid product from this part of my processcontains all the desired absorbed materials together with the absorbent.Thus the absorbent liquid is introduced to the top of the absorber andthe liquid Withdrawn from the bottom is cooled and passed to aliquid-vapor separator. The gas to be treated in my process is alsocooled and passed to` the same separator, and likewise the vapors fromthe top of the fractionator are cooled and passed to this separator. Theuncondensed gases and vapors from this separator are then the componentsof the gaseous stream passed to the absorber which is introduced to alow point thereof. The liquid material from this separator is passed tothe fractionator, and isV introduced to the top part thereof in thenature of a reiiux liquid. Undesired gases are removed from the top ofthe absorber, and the rich absorbent containing in solution the desiredconstituents of the gas charged to the process is removed from thebottom of the fractionator.

I have further found that, in the practice of a preferred modificationof my invention, the

vapor and liquid stream are preferably combined before cooling, andsubjected to cooling and condensation in admixture with each otherrather than as separate streams. Thus, I prefer to mix the aforesaidliquid from the absorber, vapor from the fractionator, and gas chargedtothe process, and subject the resultant composite mixture to a singlecooling operation, and pass the single cooled mixture to a separator.Likewise, rather than introducing the absorbent liquid directly to thetop of the absorber, I prefer to i mix it with the gas stream'leavingthe top of- 1 the absorber and to subject the resulting mixture tocooling and'condensation, This cooled mixture is then passed to aseparator, the uncondensed gas from the separator is discharged from theprocess; or further treated as may be desired, and the liquid from thisseparator is passed to the top of the absorber as the absorption liquid.

Reference will now be made to the accompanyying drawings which form apart of .this specification, and which illustrate diagrammatically bymeans of a ow sheet one arrangementl of apparatus suitable forpracticing my invention in its preferred form. It will be described incombination with a thermal alkylation process for the 'conversion oflo'w boiling aliphatic hydrocarbons to paraflins in the motor fuelboiling range, a combination which serves as an example of my inventionand one that I have found to be particularlyv desirable. However, itwill be understood that other thermal conversion processes onlykminoramounts of light oils. 1f` desired, a

suitable dehydrogenating catalyst, not shown, may be usedvin place of oralong with the cracking operation, especially when a heavier stock isbeing dehydrogenated to produce higher boiling unsaturates, but forthe'charge stocks here speciiically described the simple cracking anddehydrogenation is adequate.` The cracked material is passed throughcooler I4 to a separator or tar scrubber I5, wherein any tar-likematerialand/oz' carbon separates from the gaseous stream and is removedthrough pipe I6 and valve I1. A gaseous stream is passed from tarscrubber I through pipe and valve 2l and through cooler I9 to scrubber22, being joined by any liquid materials separated as a result ofsubsequent compression which are passed, through pipe- 30. The gaseousmaterial in scrubber 22 is passed through pipe 23 and valve 24 to acompressor 25, which increases the pressure from about r0.5 to 10 poundsper square inch gauge to about 40 to 60 pounds per square inch. Thematerial is then passed through cooler 26 and pipe 21 to scrubber 28.

Any liquid material which separates out in scrubber 28 is removedthrough pipe 30 and valve 3| to scrubber 22, as by being introduced intopipe 20. A gas stream is passed from scrubberv 28 ythrough pipe 33 andvalve 32 to a compressor 34, which increases the pressure from about 40to 60 pounds per square inch gage to about 190 to 240 pounds per squareinch gage, and compressed gas is then passed through cooler 35 and pipe35 to scrubber 31. Any liquid material which separates out in scrubber31 is removed through pipe 38 and valve 39 to scrubber 28, as by beingintroduced intol pipe v21, as shown. Light oils and other condensateswhich ultimately remain liquid in scrubber 22 can be removed from thesystem through pipe 40 and valve 4I.

A gas stream is passed from scrubber 31 through pipe 44 and valve 45 toa compressor 45 and is there compressed to about 700 to 850 pounds persquare inch gage, and is then passed through pipe 41 and valve 48 tofractionator 50.

45 Fractionator 50 may be of any suitable type may form a part of thecombination, or that l other alkylation processes may form a. part ofthe combination, with suitable modifications in any particular case aswill be readily ascertained or determined by trial by one skilled in theart in the light of the present disclosure, and that this. also appliesto charge stocks different from those specifically discussed.

Figs. 1 and 1A together illustrate the process.

In this combination, a light gaseous hydrocarbon material'such as amixture comprising ethane and propane, is passed from any desirablesource through pipe I0 and valve I I to the cracking and dehydrogenatingfurnace I2. This mixture is heated and cracked in coil I3 at a. lowsuperatmospheric pressure of the order of 5 to 30 pounds per square inchand at a temperature of 1300 to 1600 F. for a time suiilcient toform anoptimum amount oi' ethylene and propylene with 75 known to the art,comprising bubble plates and heating and cooling units to eiTectadequate fractionation in the presence of liquid reflux. A liquid isremoved from the bottom through pipe 5I and valve 52, and is passed tofractionator 53. similar to fractionator 50 but operating at about 250pounds per square inch pressure. Undesired liquid material, in this caseconsisting of C4 and heavier hydrocarbons and containing an appreciableamount of butadiene produced as one of the reaction products underconditions such as described for coil I3, is removed from the systemthrough pipe 54 and valve 55. Gaseous material which should be retainedis passed from fractionator 53 through pipe B8 and valve 51 back to thesystem, and in this case is reintroduced into pipev38. Light gases freedof heavier material pass from fractionator 50 through pipe 60 and valveSI.

It will, of course, be appreciated that other separating means thanfractionators 50 and 53 may be used, such as a suitable absorptionapparatus with auxiliary equipment, not shown. If it is not necessary ordesirable to separate heavier material at this point, such apparatus maybe eliminated completely, and the gas compressed by compressor 4B passeddirectly through pipes 41 and 82, and valve 83, to pipe 60.

When thermal cracking is employed under the conditions such as describedfor coil I3, an appreciable amount of acetylene is produced, which ispreferably removed before subsequent treatment.

-This can vbe done by passing the gases through valve 55 lto heater 60and through pipe 01 to deacetyllzer 10. These gases contain hydrogenproduced'by the previous dehydrogenation, and

' zationas by passing the material at an elevated temperature'over.bauxite. Such treatment will also remove butadiene and the like if thishas not been previously removed. The eiiluent is passed through pipe licooler 12fand pipe 13 to' scrubber 14. In order to accomplish a suitablyselective removal of acetylene without involving any appreciable amountof desired -unsaturated material in the reaction, a close temperatureconture to increase unduly can bevquickly and eiectively met byintroducing butane into the. stream trol is necessary. Any tendency ofthe temperature oi about -40 .to v-50 F. The mixture, preferably at atemperature of about -30 F., is passed to a separator |53, wherein aseparation is effected between gas and liquid phases. The liquid ispassed from separator |53 through pipe |50 and valve |55, and is sent bypump -|50 to a point near the top of the absorber |50l as absorptionliquid. The gas phase is passed from separator |53 through pipe |58, andmay be discharged from the system through valve |51, or may be processedto recover vaporized butane. 'aswill be discussed hereinafter.

A liquid containing absorbed olefins, is removed irom the bottom of theabsorber |50 through pipe |60 and is passed through pump Mi s .nd pipe|02 to cooler |53 and separator |54.y

passing through pipe'80, which isl cooled to a l suitable temperature bycooler |55 and is introduced through pipe |65. l There is also ad- I,mixed with thisimaterial a gaseous stream which passing through pipe 01,as from pipe 04 through l pipe 15 and valve 15. Valve 15 may be operatedautomatically by a temperature responsive device represented by thedashed line 11 in ypipe 1| at the exit of deacetylizer 10. Heavierhydrocarbons, such as acetylene polymers, may be removed from the systemthrough' pipe 18 and valve 19. letylene-free gases are passed fromscrubber 10 t rough pipe 80 and valve 8|. If it is not necessary toinclude scrubber 10, the eiliuent'of 10 may v be passed through pipe 82and valve 00 directly to pipe 80. When it is not necessary to employ anacetylene removal' step, gases may be .passed directly from pipe 50 topipe 00 throughby-pass 00 and valve 05. When a gaseous mixture of'a,desirable composition is available from some other source, not shown,such as an oil cracking process, it may be introduced to the process',as through pipe 05 and valve 01, either to be added to the material justdescribed passing through pipe 50, or as the entire source oi' suchmaterial.'

as may be expedient. Itmay or may Vnot be passed through thedeacetylizer 10,. as desired or as its composition requires.

When a thermal alkylation stepis a part of my process, such as isbroadly described in Frey 2,002,394l a liquid butane stream, preferablycomprising a high concentration vof isobutane, is

bons'such as ethylene and propylene, all of' ywhich are present in A themixture passing through pipe 00. In this modification of my invention,an absorber |50 is operated `at a pressure between about '100 and 800pounds per.

square inch, such as about 765 pounds per square inch. Unabsorbed gasespass from the top or the absorber |50 through' pipev |5| at 'atemperature of about 0 to 10 F., and are intimately ad mixed with theliquid .butane' absorbent introis passed from the top of fractionator|15 through pipe |15 and valve |11. The composite, intimately mixedmaterial, under a pressure somewhat higher than that existing inabsorber |50; is cooled in cooler |53 to a temperature between about -10and 35 F. generally about -15 to 30 F. in this particular case. This maybe accomplished 'by indirect heat exchange with vaporizing propane, orother cooling medium at ay temperature of about -40 F.,

as will-be readily appreciated. In vseparator |54 a separation iseffected between gasb and liquid phases. The, uncondensed Igaseousmaterial is passed through pipe |01 and valve |58 to absorber |50 atf'apointy near the bottom. The

, liquid is passed from separator |00 through pipe |60V and valve |10,and is sent byv pump |1| as a reilux liquid to fractionator |15at apoint near the tot.`

A rich absorption moved from the bottom ot iractionator |15 at atemperature of about 100 to 125 F., the bottom m and valve m to'punip infor -mtroducrmn through pipe |03t`o the alk'yiation process, to besubsequently described. If desired, the olec 'ns may be passed to thealkylation stepin a more concentrated form.' in which' case all or apart of the stream 'is removed from pipe |00 through pipe |85 and valve|00. and is Vpassed to fractionator |01.- In ira'ctionator |01 the lightabsorbed oleilns, togetherv with a part of the absorption: butane, arevaporized, theiractionating column being suitably heated at the bottom,to a temperature oi' about 190 to 240 F., while a pressure of about 250.to 400 pounds'per ,square inch is maintained. A part'of the ab sorptionliquid, which is not vaporized, is passed duced through pipe 04. .Themixture is Apassed lthrough a coolerv and condenser |00, wherein the"mixture is cooled to about -20 to -40 F. as by indirect heat exchangewith ,vaporizing prowith some other cooling medium of a tempera.

Vfrom the-bottom through pipe |00, is cooled in` and a part of theabsorption liquid, which has |00. A portion of this liquid is returnedthrough pipe |00 and valve |00 by pump' |01 to'a high point ofiractionator |01 as reflux.' Another liquid containing absorbed yoleiinssuch as ethylene and propylene. is` re' portion is reintroduced intopipe |90 through pipe |98, valve |99, pump 200, and pipe 20|. Any vaporsor gases accumulating in |94 may be discharged from the system throughpipe 202 and valve 203, or may be introduced to pipe |98 through valve205 in pipe 204.

In the case ofthe alkylation step, the butane stream entering the systemthrough pipe is passed through valve |0| and pump |02 to heating andreacting zones |04 and |05 respectively in furnace |03. This material ispumped by pump |02 at a pressure between -about 1,000 to 10,000 poundsper square inch, and is initially heated in zone or coil |04 to atemperature between about 900 and 1100 F. The olencon taining streampassing through pipe heated by ue gases in zone |06 and is passed tomanifold |01. From manifold |01 a substanti'al plurality of streams arefed into the alkylating coil, such as about 10 or 15,'or more as high as50 or 75. These are represented by the three pipes ||0, and ||2,controlled by valves ||3, |`|4 and ||5 respectively, which lead tovarious pointsof the stream iiowing through coil |05. The material isreacted at a suitable temperature and the eluent passes through pipeIIB, cooler and condenser l1, pipe ||8 and valve ||9 to a depropanizingfractionator |20. Fractionation in depropanizer |20 is aided byconventional bubble trays, not shown, and by suitable cooling means atthe top and heating means at the bottom. A gaseous stream comprising C3hydrocarbons and lower boiling material. is passed from the top of |20through pipe |2|, and may be passed through valve |22 to pipe |0 forcracking or dehydrogena'tion, which has previously been discussed, ormay be discharged from the system through pipe |23 and valve |24.

A liquid stream, comprising unreacted butane and reaction products, ispassed from the bottom of depropanizer |20 through pipe |26 and valve|21 to a debutanlzing fractionator |28, wherein Cs and heavier reactionproducts are separated from unreacted butane. The kettle is lsuitablyheated to boil out light material, and the C and heavier is recoveredthrough pipe |29 and valve |30, and may be subjected to furtherfractionation and/or other treatment, as may be desirable.

. Vaporized material is passed from the top of debutanizer |20 throughpipe |32 and cooler and condenser |33 to reflux accumulator |34. Anylight gases, if such are present, may be removed through pipe |35 andvalve |38, as desired. A portion of the condensed material is returnedto debutanizer |20 through pipe |31, valve |38 and pump |39 as reilux.Material not needed for reflux is returned tothe system by pipe |4 0"andvalve |4|, leading to pipe |00.

Even with the high pressures and low temperatures employed in theabsorber |50 and the separator |53, some of the butane absorption liquidis vaporized, AandI passes of! through pipe |58. When it is desirableto' recoverthis vaporlzed material, all or any part of the gas passingthrough pipe |50 may be passed through pipe 2|l and valve 2|| toabsorber 250 at a low point. In vabsorber 250 it is contacted with arelatively heavy absorption oil adapted to absorb the butane, which isintroduced near the top through pipe 220. Preferably the absorberoperates at an elevated pressure only slightly under that in absorber|59, and at a temperature near atmospheric, or somewhat lower. Light,unabsorbed gases are removed through pipe 2|2, and are discharged fromthe system through valve 2|3.

Rich absorption oil is removed from the bottom of the absorber throughpipe 2|4 and valvev2l, and passes through heater 2 0 to stripper 249, at

a high point thereof, and at a temperature of f about 200 to 300 F.Stripper 249 is operated at a considerably lower pressure than absorber250, such as about 20 to 50 pounds per square inch and the stripping isaided by introduction of a lean stripping gas introducednear thebottom.-

This stripping gas may be a part of the lean gas which is removedthrough pipe 2|2, and which is passed through pipe 2|1 and valve 2|8from pipe 2|2 to stripper 249. Denuded absorption oil is passed from thebottom of stripper 249 through cooler 220, pipe 22| and valve 222 to thesurge y tank as accumulator 223. From accumulator 223 lean absorptionoil isv drawn through pipe 224 bypump 225, and passed through pipe 226to the top of absorber 250. A gaseous material comprising strippinggases and recovered butane is passed from the top of stripper 249through pipe 230 and valve 23|, and is passed by compressor 232 throughcooler and condenser 233 to the butane accumulator 234. Liquid butane sorecovered is returned to absorber as a part of the absorption liquidthrough pipe 235, and valve 235, leading from accumulator 234 to pipe90. Uncondensed vapors and gases are removed from the top of accumulator234 through pipe 231 and valve 238, and are passed by recompressor 239through cooler 240 and pipe 24| to the butane recovery step, as by beingintroduced from pipe 24| into pipe 2|0.

While a particular type of thermal alkylation has been described insome` detail, other conversion processes known to the art may be used,il.'

i as aluminum chloride or sodium chloroaluminate andthe like.concentrated sulfuric acid, concen` trated hydrouoric acid, or the likeunder` conditions suited to the particular charge stock and catalystused.

One of the advantages of my invention is that,

by mixing the absorbent passing through pipe 94 with the gas passingthrough pipe |5| and subsequently cooling these materials while somixed, a distinct economy in refrigeration is attained. Notonly is itpossible to use only a single cooling unit, cooler and condenser |52 butalso I can obtain the desired low temperature and heat removal at aAdistinctly higher temperature level for the cooling medium than I wouldneed to use if the streams were separately used. Thus I v have foundthat when the two streams are separately cooled, and these streams-havethecompositions just described, it is necessary to use a cooling mediumatA a temperature of'about 120 F. to accomplish the same result aspreviously described in connection with the use of a cooling medium at atemperatureof about 40 as described. Likewise, in connection with thefrom the spirit of the disclosure. 'I'he restrictions given ini thepreceding example and description of the drawings need not necessarilybe used as limits forall particular'operations or sets of conditions.since they' are presented-primarily as being adapted to one particularset of conditions. It will be understood that the tlow diagram isschematic only and that additional pieces of equipment, such asadditional tarandcarbon removers, pressure gages, valves, pumps, heatexchangers, reiiux lines and accumulators, heaters and coolers, and thelike will be necessary for any particular installation, and can besupplied to meet the requirements of any particular case Y by anyoneskilled in the art. Essential pieces of equipment and conditions havebeen described and their functions and modifications discussed 'v insuilicient detail to serve as eflicient guides.

I claim: I

l. A process for separating heavier hydrocarbons from normally gaseousmixtures containing such hydrocarbons along with not more than 50 percent by volume of lighter gases'in a separating means comprising aseparator, an absorber and a fractionator, which comprises passing sucha normally gaseous mixture in admixture with a liquid stream from a lowpoint of said absorber and a gas stream from a high. point of saidfractionator to said separator, passing a gas stream from said separatorto a low point of said abscrber, introducing an absorption liquid at ahigh point of said absorber, withdrawing uncondensed lighter gases froma high point of said absorber, passing a liquid stream from the afore- Ysaid separator as a reilux liquid to a high point of said fractionator,and recovering from a low point of said fractionator a liquid comprisingsaid absorption liquid and absorbed heaviery hydrocarbons. i I

2. I n the separation of ethylene and heavier hydrocarons from methaneand lighter gases.' the steps which comprise admixing a gaseous mixtureof said materials with a liquid stream from the bottom of an absorberand a gaseous stream from the top of a fra'ctionator, cooling theresultant mixture and passing the cooled mixture to a separator, passinggases from said separator to the bottom of said absorber, introducingliquid butane to the top o'f said absorber as an absorbent liquid andremoving unabsorbed gases .and vapors from the top of said absorber anddis- 1 charging same from the system, passing'a liquid rial to areaction zone, passing a normally gas-- eous mixture comprising oleilnsand gases lower boiling than C: hydrocarbons to said separating means.admixlng said normally gaseous mixture with a gas passing from the topof said fractionator and with a liquid passing from the bot- -tom ofsaid absorber, cooling the resultant admixture to a low s ubatmosphericAtemperature and passing the cooledl mixture to a separator,

point of said fractionator. f l

7. In the process of claim 6, contacting the` gas passing a gaseousmaterial from said separator to a ylow point of said absorber,introducing said sorbed gaseous olens, passing said liquid to the'aforesaid reaction zone, and vconverting butanes and olens in saidreaction zone to form higher boiling hydrocarbons.

4. AA process for reacting butane with normally gaseous unsaturatedhydrocarbons by!y alkylation which comprises passing a normally gaseousmixture comprising such unsaturated hydrocarbons along with methane andhydrogen to a separating means comprising an absorberend a fractionator,admixing wth said gaseous mixture a liquid from the bottomV of saidabsorber and a gas from the top of said ira'ctionator, cooling theresultant admixture toa subatmospheric temperaturenotlessthan 50 F. andpassing the same to a separator, passing uncondensed gases fromsaidseparator to a low point of said absorber, passingv a condensed liquidfrom said separator as a reflux liquid to a high ypoint of saidunsaturated hydrocarbons to form higher molecular weight hydrocarbons.y. y

5. The process of claim 4; wherein said liquid comprising butane ispassed to a fractionating means, separating therein a liquid fractioncomprising a portion of' said butane and returning same as a part ofsaid absorption liquid, separating also a fraction comprising saidabsorbed unsaturated hydrocarbons along with a further portion of saidbutane, and subjecting the last said fraction to said alkylatingconditions.

6. In the separation of C2 and heavier hydro-v carbons from methane andlighter gases, the improvement which comprises passing a gaseous mixtureof such materials to a separating means comprising an absorber and afractionator, withdrawing a liquid stream `from a low point of saidabsorber, withdrawing a gas stream from a high point oisaidfractionator, admixing said liquid and gas streams and said gaseousmixture, cooling the resultant admixture to condense a part of thevaporous constituents thereof, passing said cooled mixture to a firstseparator. passing a gas stream from said separator to a low point ofsaid absorber. removing a gas stream from a high point of said absorber,admixing therewith a liquid absorption medium, cooling the resultantmixture to condense vaporous portions. thereof and passing said cooledmixture to a second separator. passing a. gas from said second separatorand discharging said gas from the system,l passing a liquid from saidsecond separator to a high point of said absorber, passing a liquid fromsaid ilrst separator to a high point of said fractionator, supplyingheat to the bottom of said fracfrom a inwV tionator. and withdrawing aliquid dischargedl from said second separator with a heavy absorptionmedium, and passing hydrocarbons recovered from said heavy absorptionmedium to the aforesaid process as a part of said absorption medium. I

8. A process for converting saturated hydrocarbonshaving two and morecarbon atoms per' molecule into higher molecular weight hydrocarbons,which comprises subjecting 'an ethanepropane mixture to a pyrolysistemperature under a low pressure for a period of time sulllcient toproduce low boiling unsaturated hydrocarbons predominantly ethylene andpropylene, separating from the eiiiuent pyrolysis products having fourand more carbon atoms per molecule and discharging same from the system,passing lower boiling material from said eiiiuent to a separating meanscomprising an absorber and a fractionator, passing also to saidseparating means as an absorbent liquid a low boiling hydrocarbonmaterial of at least four carbon atoms per'molecule Aand introducingsame as a liquid to a high point of said absorber at an absorptiontemperature and pressure, discharging unabsorbed gases from saidabsorber, removing a liquid from the bottom oi said absorber, removing agaseous mixture from the top of said fractionator, admixing said gaseousmixture, said liquid, and said lower boil-l ing material, cooling theresultant admixture to a low subatmospheric temperature to condense apart of the vaporous constituents thereof, passing the cooled mixtureAto a gas-liquid separator, passing a gaseous material from saidseparator to a low point of said absorber, passing a liquid materialfrom said separator as a reflux liquid to the top of said fractionator,removing from a low point of said iractionator a. liquid comprising saidabsorbent liquid and said low boiling unsaturated hydrocarbons, andtreating the last said liquid under conversion conditions to form highermolecular weight hydrocarbons.

9. A process for converting low-boiling paraillns of at least fourvcarbon atoms per molecule along with gaseous olefin hydrocarbons intohigher boiling hydrocarbons, which comprises passing a low-boilinghydrocarbon material containing paraiilns of at least four carbon atomsper molecule as an absorption liquid to an absorber, passing a normallygaseous mixture comprising oleflns and gases lower boiling than C:hydrocarbons to a separator, 'passing a gaseous mixture from saidseparator to a low point of said absorber, discharging unabsorbed gasesfrom said absorber, passing arich absorption liquid from said absorberto said separator, passing a liquid mixture from said separator to afrac# .tionator as a reiiux, passing a gaseous mixture from saidfractionator to said separator, removing from the bottom of saidfractionator a liquid

